The present invention relates to a semiconductor device including a capacitor element that uses a ferroelectric or a high-dielectric as a material of a capacitor insulating film.
In recent years when demands for processing and storing a large amount of data are increasing in association with developments in digital technologies, electronic equipment grows more sofisticated and miniaturization of elements of semiconductor devices used therein progresses rapidly.
In association, in order to realize higher integration of dynamic random access memories (DRAMs), techniques have been widely developed in which high-dielectrics are used as capacitor insulating films instead of conventionally-used silicon oxide or silicon nitride (see, for example, Japanese Patent Application Laid Open Publication No. 2002-198498). Further, aiming at reducing to practical use nonvolatile RAMs capable of high speed writing and high speed reading with low operation voltage, which have been previously unatainable, research and development for ferroelectric films having spontaneous polarization are promoted.
The above gazette discloses that the external forms of capacitor elements are shaped into cubs such as columns, cylinders so that the capacitor value of each capacitor element is ensured while implementing miniaturization, namely, reducing the area (projection area) on a chip.
In the case where a high-dielectric or a ferroelectric is used as a material of a capacitor insulating film, it is necessary to perform annealing under an oxidizing atmosphere at a temperature of 700° C. to 800° C., which is a temperature for crystallization of the high-dielectric or the ferroelectric composing the capacitor insulating film, after formation of the capacitor insulating film. Accordingly, precious metals excellent in thermal resistance and oxidation resistance are used in general as materials of the electrodes in each capacitor element.
However, in the case where upper and lower electrodes made of a precious metal such as platinum (Pt), iridium (Ru) are formed into a solid of a column shape or of a concave shape in section formed in a concave portion in the underlying layer, the coverage at the edges or the corners of the solid becomes low, and accordingly, the thickness thereat is liable to be small. For this reason, migration is caused at a local part having a smaller thickness, which leads to breakage due to tensile stress at the annealing.